Light-transmitting metal oxides are used in semiconductor devices. For example, conductive metal oxides (hereinafter referred to as oxide conductors) such as indium tin oxide (ITO) are used as transparent electrode materials needed in display devices such as liquid crystal display devices.
In addition, light-transmitting metal oxides also attract attention as materials having semiconductor properties. For example, In—Ga—Zn—O-based oxides and the like are expected to be used as semiconductor materials needed in display devices such as liquid crystal display devices. In particular, they are expected to be used for channel layers (also referred to as channel formation layers) of thin film transistors (also referred to as TFTs).
Metal oxides having semiconductor properties (hereinafter referred to as oxide semiconductors) are increasingly expected as materials which replace or surpass amorphous silicon used in display devices and the like.
Further, oxide conductors and oxide semiconductors have light-transmitting properties. Therefore, by forming TFTs with the use of these materials, light-transmitting TFTs can be formed (for example, see Reference 1).
Furthermore, TFTs including oxide semiconductors have high field-effect mobility. Therefore, driver circuits in display devices or the like can be formed using such TFTs (for example, see Reference 2).
[Reference]
    Reference 1: T. Nozawa, “Transparent Circuitry”, Nikkei Electronics, No. 959, Aug. 27, 2007, pp. 39-52.    Reference 2: T. Osada et al., “Development of Driver-Integrated Panel using Amorphous In—Ga—Zn—Oxide TFT”, Proc. SID '09 Digest, 2009, pp. 184-187.